United Airlines resumes Boeing 787 flights

United Airlines is getting its 787s back in the air, beginning Monday with Flight 1 from Houston to Chicago.

The planes are flying again after being grounded for four months because of smoldering batteries on 787s owned by other airlines. The incidents included an emergency landing of one plane, and a fire on another. Federal authorities lifted the grounding order on April 19 but it has taken Boeing, which makes the plane, and the airlines a few more weeks to fix most of them.

The incidents never caused any serious injuries. But the January grounding embarrassed Boeing and disrupted schedules at the eight airlines that were flying the planes. The company had delivered 50 worldwide when the model was grounded.

United is the only U.S. airline currently flying the 787. The grounding forced it to delay planned international flights and reduced first-quarter earnings by $11 million. Other airlines, including Japan Airlines and South America’s LATAM Airlines Group, also said profit took a hit. LATAM said it still had to make payments on the plane and pay for crews and maintenance. It expects to resume flying soon.

United’s first 787 flight departed Bush Intercontinental Airport in Houston at 9:14 a.m. Pacific time and arrived at O’Hare International Airport in Chicago at 11:13 a.m.

Passengers didn’t appear to be too worried. “We saw strong demand for the flight from the first weekend it opened for sale,” said United spokeswoman Christen David.

Ethiopian Airlines resumed flying 787s on April 27, and Air India and Qatar have also restarted flights. All Nippon Airways and Japan Airlines have both said they expect to restart 787 flights on June 1.

United is planning to use 787s on shorter domestic flights before resuming international flights on June 10 with new Denver-to-Tokyo service as well as temporary Houston-to-London flights. It’s adding flights to Tokyo, Shanghai and Lagos, Nigeria, in August.

Those long international flights are the main reason the 787 exists. Its medium size and fuel efficiency are a good fit for long routes. Starting with shorter domestic flights “will give us a period to ramp up full 787 operations,” David said.

United Continental Holdings Inc. now has six 787s. United expected to have four fixed by Monday, with the other two getting batteries modified in coming days.

The 787 uses more electricity than any other jet. And it makes more use of lithium-ion batteries than other jets to provide power for things like flight controls and a backup generator when its engines are shut down. Each 787 has two of the batteries.

Boeing Co. never did figure out the root cause of the battery incidents. Instead, it redesigned the battery and its charger. The idea was to eliminate all of the possible causes, 787 chief engineer Mike Sinnett said in an online chat on Thursday where he and a Boeing test pilot took questions about the plane.

The changes include more heat insulation between each cell and charging the battery to a lower maximum voltage.

Boeing said that as of Sunday, 45 planes had gotten the battery fix out of 50 that were in service when they were grounded. It said it will finish the modifications by the end of May.

Boeing never stopped making 787s, but deliveries were halted. They resumed last week, and Boeing has since delivered two planes, both with the new battery system.